append_left(other:DS_LINEAR[G])-- Add items of other to left of internal cursor position.
-- Keep items of other in the same order.
-- Do not move cursors.require
other_not_void: other /=Void
not_before:notbeforeensure
new_count:count= oldcount+ other.count
same_order:(not other.is_empty)implies(item(oldindex) = other.first)

append_right(other:DS_LINEAR[G])-- Add items of other to right of internal cursor position.
-- Keep items of other in the same order.
-- Do not move cursors.require
other_not_void: other /=Void
not_after:notafterensure
new_count:count= oldcount+ other.count
same_order:(not other.is_empty)implies(item(index+1) = other.first)